The field of the present invention is sensor apparatus for pulse oximetry.
Pulse oximetry provides a means of non-invasively measuring oxygen saturation of arterial blood for purposes of monitoring and evaluating the physical condition of a patient under medical care and to avoid patient hypoxemia. Pulse oximetry functions by positioning a pulsating arterial vascular bed (such as that in a patient's finger or ear lobe) between a two-wavelength light source and a detector. The pulsating vascular bed, by expanding and relaxing, creates a change in the amount of light passing through at each wavelength. Oxyhemoglobin and reduced hemoglobin differ in their light absorption characteristics. The varying amounts of light from the light source passing through the vascular bed are received by the detector as a waveform, whose signal is processed electronically by a pulse oximeter into a measurement of arterial hemoglobin oxygen saturation. Such oximeters are described, e.g., in U.S. Pat. No. 4,824,242, which is incorporated herein by reference.
A sensor apparatus, containing the light source, the detector, and connecting wiring or cables, is used to position the light source and detector components in proper relation to each other at an appropriate body site. For example, the light source may be positioned on one side of a patient's finger, with the detector positioned directly opposite the light source on the other side of the finger. Cables and wiring connect the light source and detector at the patient site, and transmit the waveform signal to the oximeter for processing. The light source, the detector, and their connecting wires have typically been secured to a support which facilitates proper placement of the light source and detector in relation to each other and at the desired site on the patient. For example, the light source, detector, and connecting cables have been attached to a flexible wrap material, which is wrapped around and temporarily secured to a body site, such as a finger. Such a sensor apparatus generally is a single use, disposable item due to its direct contact with the patient. A drawback of such a disposable oximeter sensor apparatus is its relatively high cost per use.
Alternately, sensor components (including the light source, detector, and connecting wires) have been mounted and sealed into, for example, a molded shell which can be disinfected and reused in multiple applications and among different patients. However, such a reusable oximeter sensor apparatus must be relatively durable to withstand multiple attachments, and the sensor components must be sealed within the molded shell so that application of liquid disinfectant to the surface of the shell by wiping or immersion will not result in moisture reaching and damaging the sensor components. Further, the molding process must be accomplished without the use of excess or prolonged high temperature which would damage the sensor components.
As a result, existing reusable oximeter sensors have been relatively costly since their manufacture is labor and/or time intensive. For example, such reusable sensors have been manufactured by first molding two shell halves, enclosing the sensor components between the halves in proper position, and then gluing the halves together to seal out moisture, a time and labor intensive process.
Alternatively, reusable oximeter sensors have been manufactured utilizing a silicone overmolding process, in which the sensor components are positioned within a first premolded silicone half shell, and then encased and sealed as silicone is injected in an overmolding step to complete the molded shell. Due to the properties of the silicone used, the two portions of the completed molded shell seal to each other. However, the cycle time for this overmolding operation is typically 25-40 minutes, depending on the specific type of silicone and its curing temperature. The curing temperature must be kept low, resulting in the relatively long cure time, since excess heat will destroy the cable and optical components which comprise the active sensor components. Further, given such long cycle times, each base mold can produce only relatively few molded sensors per day, requiring large capital expenditures for multiple base molds or tools to achieve significant daily volume production of sensors.